1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main′ pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole passes a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). An airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium causes the slider to slightly fly over the surface of the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. The unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent the occurrence of unwanted erasure.
In order to prevent the occurrence of unwanted erasure induced by a skew and achieve higher recording densities, it is effective to configure the main pole so that the thickness of its portion near the medium facing surface decreases with increasing proximity to the medium facing surface, and also provide a write shield that has an end face located in the medium facing surface and surrounding the end face of the main pole.
In a magnetic head including the write shield, there is typically provided a return path section for connecting the write shield to a part of the main pole located away from the medium facing surface. The write shield, the return path section and the main pole define a space for a part of the coil to pass therethrough. The write shield and the return path section have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than a direction perpendicular to the plane of the recording medium, thereby preventing the magnetic flux from reaching the recording medium. The write shield and the return path section also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized a part of the recording medium to flow back to the main pole.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of the trailing-side edge of the end face of the main pole located in the medium facing surface. In order to define the position of the end of the record bit accurately, it is thus important that the write shield include a trailing shield which is located on the trailing side relative to the main pole.
With increases in frequency of write signals to achieve higher recording densities, it is required of the magnetic head that the write current flowing through the coil should exhibit a rapid rise. To meet such a requirement, it is effective to reduce the length of a magnetic path that passes through the write shield, the return path section and the main pole. To achieve this, it is effective to reduce the distance between the medium facing surface and an end of the coil that is closest to the medium facing surface.
U.S. Pat. No. 8,385,019 B1 discloses a magnetic head having the following features. The magnetic head includes a main pole, a coil, a write shield and a return path section. The main pole has a top surface including an inclined portion and a flat portion, the inclined portion being located closer to the medium facing surface than is the flat portion. The inclined portion is inclined with respect to a direction perpendicular to the medium facing surface. The flat portion extends in a direction substantially perpendicular to the medium facing surface. The write shield includes a trailing shield. The coil includes a coil element located on the trailing side relative to the main pole, the coil element extending to pass through a space defined by the main pole, the trailing shield and the return path section. The coil element has a first inclined surface inclined with respect to the medium facing surface. The trailing shield has a second inclined surface. The second inclined surface includes a first portion opposed to the inclined portion of the top surface of the main pole, and a second portion opposed to the first inclined surface of the coil element. This magnetic head allows a reduction in length of the magnetic path passing through the trailing shield, the return path section and the main pole.
However, the magnetic head disclosed in U.S. Pat. No. 8,385,019 B1 has room for improvement in the following respects. In the manufacturing method for this magnetic head, an insulating layer is formed to cover the first inclined surface of the coil element, and then a magnetic layer to become the trailing shield is formed on the insulating layer by plating. In this case, a region that lies below the magnetic layer and coincides with the magnetic layer when viewed in a direction perpendicular to the top surface of the substrate includes a first region in which the coil element is absent and a second region in which the coil element is present. In the first region, the magnetic layer exhibits crystal growth in the direction perpendicular to the top surface of the substrate. In the second region, the magnetic layer exhibits crystal growth in the direction perpendicular to the first inclined surface. As a result, the trailing shield includes two portions having different crystal growth directions. Such a trailing shield has a greater number of grain boundaries and defects. In such a trailing shield, magnetization rotation and domain wall displacement cannot smoothly proceed, and leakage magnetic field is thus likely to occur from the end face of the trailing shield toward the outside of the medium facing surface. This results in the problem of the occurrence of unwanted erasure.
The aforementioned problem occurs also when the coil element has a front end face parallel to the medium facing surface, instead of the first inclined surface.